Identity documents are often processed in processing equipment configured to perform a variety of processing operations on the identity documents. For example, the processing can include the addition of information to the document that is unique to the intended holder of the identity document. The types of identity documents which are often processed include plastic and composite cards, such as financial (e.g. credit and debit) cards, drivers' licenses, national identification cards, and other cards, as well as passports.
For large volume, batch processing of identity documents, systems are known that employ multiple processing modules to process multiple identity documents at the same time and reduce the overall per document processing time. Examples of such systems include the systems disclosed in U.S. Pat. Nos. 6,902,107 and 6,783,067, and the DataCard MaxSys, 9000 and DPL4000 series systems available from DataCard Corporation of Minneapolis, Minn.
For smaller volume processing of identity documents, for example one at a time processing, desktop processing machines are known. Examples of desktop processing machines include the SP 75 and SP 55 machines, and the DPL40 machine, each of which is available from DataCard Corporation of Minneapolis, Minn.
In identity document processing equipment, a number of ribbons are used to process the documents. Ribbons that are used include multi-color and monochromatic print ribbons, and webs that are used to apply various topcoat and protective layers to the documents.
In many ribbons, it is important that uniform tension be maintained on the ribbon to optimize the resulting processing operation that uses the ribbon. For example, when thermal printing on a card, it is desirable to maintain uniform tension on the print ribbon, which translates into uniform ribbon and card motion, which translates into improved print quality.
With reference to FIG. 1, a known printer IO that is used in card processing equipment is schematically illustrated. The printer 10 includes a card processing mechanism 12 in the form of a thermal print head that performs thermal printing on plastic cards 16. A platen 14 in the form of a backing roller is positioned opposite the print head 12 to support the cards during printing. Cards are driven one by one into the nip between the print head 12 and the platen 14 by a suitable drive mechanism 18, for example a pair of drive rollers. A supply roll 20 supplies print ribbon 22 for use during the print process, and a take-up roll 24 takes up used print ribbon. The print ribbon 22 follows a ribbon path between the supply roll 20 and the take-up roll 24 and past the print head 12, guided by a plurality of ribbon guides 26.
It is common to have clutches or brakes attached to the supply and take-up rolls for tensioning the ribbon 22 and to account for differences in speed or distance traveled by the ribbon relative to the card or the supply and take-up rolls. Clutches/brakes 28, 30 are illustrated in dashed lines on the supply and take-up rolls in FIG. 1. Since the clutch or brake parts are often attached to the spindles of the supply and take-up rolls, the amount of tension that is delivered to the ribbon will change significantly depending on the amount of ribbon on the rolls. A friction roller is commonly used on the take-up side to control ribbon motion. But a friction roller prevents accurate motion of the ribbon when the ribbon is reversed in direction, as the friction roller tends to loosen the roll and the friction roller can slip.
Further, since the ribbons are consumable items in the processing equipment, it is desirable to be able to track how much ribbon has been used and monitor how much ribbon remains to be used.